1. Field of the Invention
The present invention relates to a battery charging system for interrupting the charging of a battery when the power supply suffers a failure while the battery is being charged and continuing the charging of the battery when the power supply recovers from the failure, and an electric vehicle which has as an energy source the battery which is controlled by the battery charging system.
2. Description of the Related Art
Many electric vehicles which has as an energy source a vehicle-use battery having a high voltage of 288 V or the like carry a battery charger that allows the battery to be charged conveniently at home.
When the vehicle-carried battery charger charges the battery, an input terminal of the vehicle-carried battery charger is electrically connected to an external power supply and an output terminal thereof is electrically connected to the battery. A charging control computer (charging controller) is connected to a control terminal of the vehicle-carried battery charger for controlling the charging of the battery.
The charging control computer itself is energized by an auxiliary battery such as a vehicle-carried battery having a low voltage of 12 V or the like for energizing electronic parts including ICs. In order to distinguish from such an auxiliary battery, the battery as the energy source for the electric vehicle is referred to as a main battery.
The auxiliary battery is charged by a current supplied from the main battery through a DC/DC converter.
It has been found that when the external power supply suffers a failure while it is charging the main battery, if the power supply failure continues for a long time, then the auxiliary battery is discharged to the extent that its capacity becomes nil and hence the capacity of the main battery is also eliminated because the charging control computer is continuously operated. Once the capacity of the main battery is eliminated, even when the power supply recovers from the failure, the main battery will not start being charged until the auxiliary battery is recharged.
One solution is to automatically shut down the charging control computer when the external power supply suffers a failure. Because the charging control computer is automatically shut down, the auxiliary battery is prevented from being fully discharged. However, even when the power supply recovers from the failure, the auxiliary battery does not resume its charging, and will not be fully charged. It is important to solve these problems because batteries on electric vehicles are usually charged at night and it normally takes several hours for the batteries to be fully charged.